Seismic Wave Scattering Analysis using a 3D Boundary Element Method on Topographic Irregularities

摘要

Amplification of seismic waves in the presence of topographic irregularities is often advocated as one of the possible causes of intensification of damage during earthquakes. Furthermore, topographic site effects may play a significant role in the activation of landslides and rockslides during earthquakes. In this research, topography effects of canyon sites are analyzed using a three-dimensional boundary element procedure. Effects of modeling parameters (free-field and canyon length) are investigated in order to obtain accurate results. It is shown that the free-field length has little effect in comparison with the canyon length to obtain accurate results. Some general rules for three-dimensional modeling of seismic wave scattering with boundary element method are achieved. Also effects of different wave parameters (frequency and direction), material properties (damping ratio and Poisson's ratio) are investigated. It is demonstrated that material properties, wave incident angle and frequency have considerable effects on the wave scattering problems. The system with damping may induce large displacements in the side of the canyon located in the wave arriving direction in comparison to system without damping. Wave parameters (direction and frequency) affect on the pattern of the displacement variation across the canyon on the other hand material properties (damping and Poisson's ratio) don't affect on the pattern of the displacement variation. As the wavelength of the input wave becomes comparable to the characteristic length of the canyon, more complicated wave pattern of the scattered field is expected.